PCB Blog - The influence of integrated passive components on the development of PCB board technology

The integrated passive component technology developed by PCB board technology can integrate a variety of electronic functions, and has the advantages of miniaturization and improved system performance to replace bulky discrete passive components. The article mainly introduces the development of integrated passive component technology, and the use of IPD film technology to realize the processing of capacitors, resistors and inductors, and discusses the influence of IPD on the development of PCB board technology.

1. Introduction
With the development of electronic technology, the integration of active electronic components has been greatly improved after semiconductors have been made from micron processes to nanometers, and the demand for passive components with active components has increased significantly. The market development trend of electronic products is light, thin and short. Therefore, the improvement of semiconductor process capability has greatly increased the number of active components in the same volume. In addition to the substantial increase in the number of supporting passive components, more space is needed to place these passive components. Therefore, the size of the overall packaged device will inevitably increase, which is very different from the development trend of the market. From the perspective of cost, the total cost is proportional to the number of passive components. Therefore, under the premise that a large number of passive components are used, how to reduce the cost and space of passive components, or even improve the performance of passive components, is currently an important issue. one of the topics. IPD (Integrated Passive Devices) technology can integrate a variety of electronic functions, such as sensors, RF transceivers, MEMS, power amplifiers, power management units and digital processors, etc., to provide compact integrated passive devices IPD products have the advantages of miniaturization and improved system performance. Therefore, whether it is reducing the size and weight of the entire product, or adding functionality within the existing product volume, integrated passive component technology can play a great role. In the past few years, IPD technology has become an important implementation of system-in-package (SiP), and IPD technology will pave the way for integrated multi-functionalization "beyond Moore's Law"; at the same time, the processing of PCB boards can introduce IPD technology, through the integrated advantages of IPD technology, can bridge the widening gap between packaging technology and PCB board technology. IPD integrated passive component technology has developed from the initial commercial technology to the present to replace discrete passive components, and has grown steadily driven by industries such as ESD/EMI.RF, high-brightness LED, and digital hybrid circuits.

2. Introduction of thin film IPD technology
IPD technology can be divided into thick film process and thin film process according to the process technology. Among them, the thick film process technology includes low temperature co-fired ceramic LTCC (Low Temperature Co-fired Ceramics) technology using ceramic as substrate and PCB based on HDI high density interconnection printed circuit boards embedded passive components (Embedded Passives) technology; and thin film IPD technology, using commonly used semiconductor technology to make circuits and capacitors, resistors and inductors. LTCC technology uses ceramic materials as substrates, embeds passive components such as capacitors and resistors in the ceramic substrate, and forms integrated ceramic components by sintering, which can greatly reduce the space of components. However, as the number of layers increases, the difficulty and cost of manufacturing increase. Therefore, LTCC components are mostly used for circuits with a specific function; the PCB board technology of HDI embedded components is usually used in digital systems, in which it is only suitable for distributed welding capacitors and medium and low precision. Resistors, as the size of components shrinks, SMT equipment is not easy to handle too small components. Although the embedded printed circuit board technology is mature, the product characteristics are poor, and the tolerance cannot be accurately grasped, because the components are buried in the multi-layer board, and it is difficult to replace or repair and adjust after a problem occurs. Compared with LTCC technology and PCB Board embedded component technology, thin film IPD technology of integrated circuits, with high precision and high repeatability. The advantages of small size, high reliability and low cost are bound to become the mainstream of IPD in the future. This article will mainly introduce the thin film IPD technology.

3. Development status of thin film integrated passive component technology
Thin-film IPD technology uses thin-film processes such as exposure-development-coating-diffusion-etching. This process can produce various resistors, capacitors, and inductance components, as well as low-inductance ground planes and transmission lines that connect passive components. The thin-film structure is suitable for Manufactured on the same carrier substrate material, the process must not only meet the required component performance and accuracy indicators, but also not complicated, and the number of masks (usually 6 to 10) is required. Each passive component usually occupies less than 1 mm2 area in order to be able to compete with discrete components of surface mount technology in terms of area and cost. According to the existing IPD structure, the development manufacturers are introduced as follows:
(1) Telephus
The IPD developed by Telephus uses a thick copper process, which can improve performance for lines with only passive components. Reduce cost and reduce size, such as filters and dividers, thick copper metal layers (10 mm) and silicon insulating surfaces enable wireless Communication systems and integrated RF modules have high performance, and low-k materials are suitable for reducing parasitic capacitance between metal layers.
(2) IMEC
IMEC's thin film technology also uses electroplated copper as the connection line, BCB as the dielectric layer, and the Ni/Au layer as the metal for the final connection surface, using up to 4 metal layers.
(3) Dai Nippon
The IPD resistors developed by Dai Nippon are mainly Ti/Cr, and the capacitors are formed by anodizing to form Ta2O5. The inductors are designed with microstrip lines and spiral inductors.
(4) SyChip
The IPD developed by SyChip uses TaSi as the resistance material, the dielectric material of the capacitor is Si3N4, the upper electrode is Al, the lower electrode is TaSi, and the inductor and circuit materials are all made of aluminum. Some companies are using MEMS process to develop IPD.

4. Structure and process of thin film integrated passive component technology
The difference between the thin film process and the thick film process lies in the thickness of the resulting film. Generally, the thickness of the so-called thick film is more than 5μm~10μm, while the thickness of the thin film process is about 0.01 μm~1 μm. If a thin-film process is used to form resistors, capacitors and inductors at the same time, different processes and materials are required to make them. Thin-film technology is applied in the semiconductor integrated circuit manufacturing process, and the technology development is quite mature. Therefore, when integrating the process, it is only necessary to pay attention to the compatibility of materials between different components, and then the process design can be achieved. In general, thin-film IPD integrated passive components can be fabricated on different substrates due to different product applications. The substrate can be selected from silicon wafers, alumina ceramic substrates, and glass substrates. Thin-film IPD integrated passive component technology can integrate thin-film resistors,capacitor and inductor in one, its process technology development, including: lithography processing technology, thin film deposition processing technology, etching processing technology, electroplating processing technology, electroless plating processing technology. In addition to the integration of passive components, the process of active components can also be combined on silicon wafers to integrate passive components with active component circuits to achieve multi-functional requirements.
(1) Thin film resistor processing
Thin film resistors are usually fabricated by sputtering process, the resistance material is electroplated on the insulating substrate, and then photoresist and etching techniques are used to process the resistance pattern to obtain the designed resistance value. In the application of materials, it is necessary to consider the TCR of the resistance material, that is, the resistance change rate at different temperatures. The formation methods of thin film resistors include vacuum evaporation, sputtering, thermal decomposition and electroplating, and commonly used resistor materials include three types of single-component metals, alloys and cermets.
(2) Film capacitor processing
Because MIS (Metal-Insulator-Semiconductor metal-insulator-semiconductor structure) film capacitors use semiconductors as the bottom electrode, the capacitor itself has parasitic resistance, which reduces the resonant frequency of the element and cannot be applied to frequencies above 200 MHz, so high-frequency Applications must choose MIM (Metal-Insulator-Metal metal-insulator-semiconductor structure) film capacitors. MIM capacitors can reduce the parasitic resistance value, thereby increasing the resonant frequency of the component, and the resonant frequency depends on the natural frequency of the dielectric material. Like thin film resistors, thin film capacitors need to account for the rate of capacitance change, and so does the dielectric constant. In addition, it is necessary to pay attention to the surface roughness Ra<0.3 μm of the substrate. If the roughness Ra value exceeds the specified range, the dielectric layer is easily penetrated by the hill lock of the bottom electrode, resulting in a short circuit.
(3) Thin-film inductor processing
The thin-film inductor process is similar to the resistor process, but the main design consideration is how to reduce its parasitic capacitance and improve the quality factor (Q) of the component. Due to the ratio of inductance characteristics, considering the need to reduce its DC impedance to improve the Q value, the inductor wire The thickness of the film must be between 5 μm and 10 μm, so the inductance wire is usually formed by electroplating in the process to meet the requirements. The surface roughness of the substrate will affect the characteristics of the thin-film inductor, especially at high frequencies, too high surface roughness will easily lead to an increase in noise and a decrease in high-frequency characteristics, so the selection, fabrication and processing of the substrate will affect the to the efficiency of the entire thin film element.

5. The impact of IPD technology on the development of PCB board technology
With the advancement of technology, PCB printed circuit boards are developing in the direction of higher precision and higher density, and are gradually highly integrated with the IC packaging field. The integration of passive components conforms to the development trend of today's electronic systems. IPD technology has become a An important implementation of System-in-Package (SiP). IPD integrated passive component technology has high wiring density, small size, light weight; high integration, can embed passive devices and active chips such as resistors, inductors, capacitors; good high-frequency characteristics, can be used in microwave and millimeter wave fields Etc. The thin-film IPD integrated passive component technology is applied to PCB board processing to save packaging area, improve signal transmission performance and reduce costs. In order to improve reliability and other purposes, through the integration advantages of IPD technology, bridging the growing gap between packaging technology and PCB board technology, it can effectively reduce the volume and weight of electronic complete machines and systems, and has broad market prospects. For IPD integrated passive components, PCB board processing can be used. Metal, diamond, ceramic or aluminum, silicon carbide composite materials with high thermal conductivity can be used as substrates to manufacture high-density and high-power multilayer circuit substrates. At the same time, IPD passive integrated PCB should be strengthened. Process improvement of board substrate. The improvement of material properties and cost reduction, as well as the accelerated application in the fields of microwave communication, high-density integration and high-power.

6. Conclusion
Thin-film IPD integrated passive component technology can integrate a variety of electronic functions, has the advantages of miniaturization and improved system performance, and can replace bulky discrete passive components. At the same time, the processing of PCB boards can introduce IPD technology. Through the integrated advantages of IPD technology, the expanding gap between packaging technology and PCB board technology can be bridged. The rapid development of thin-film IPD integrated passive component technology has brought passive integration technology into the stage of practicality and industrialization. A new generation of passive components and related integrated technologies will be widely used in aerospace, medical, industrial control and communications, etc. The electronics industry in various fields, therefore, the development of IPD technology is of great significance to the development of the PCB board enterprise itself and the enhancement of the competitiveness of the domestic industry.